HOW IT LOOKS/FEELS/SMELLS: It's a slippery, slightly viscous liquid with a fruity floral scent

WHY WE LIKE IT:There's a reason this silicone-based serum, launched in 1990, is still insanely popular—it never disappoints. It delivers intense shine, makes damaged hair appear healthier, and makes frizzy hair look supersmooth. It even works on thin, frizzy hair. "All you need is a tiny drop, like the size of a pea," says one fine-haired Allure editor. "Run it from midlength to ends." You can either let it air-dry or use a blow-dryer, but if you choose the latter, make sure to wash your hands first so you dont get any more of the serum in your hair or along your roots.